This kind of bipolar pulsed power supply is used, for example, in a sputtering apparatus for forming a predetermined thin film on the surface of a substrate to be processed. There is known one which comprises: a rectifying circuit for supplying DC power; and a MOSFET bridge circuit which is connected to the positive and the negative output ends of the rectifying circuit and which is made up of four switching elements. Each of the switching elements is appropriately operated to thereby apply an arbitrary pulsed voltage to a pair of targets which are output ends (electrodes) by alternately switching polarity at a predetermined frequency. By thus switching the targets alternately to anode electrode and cathode electrode, glow discharge is caused to be generated between the anode electrode and the cathode electrode, and a plasma atmosphere is formed to sputter each of the targets. According to this arrangement, there is an advantage in that the electric charges to be accumulated on the surface of the targets are canceled by applying the voltage of opposite phase, thereby obtaining a stable electric discharge (see, e.g., patent document 1).
It is known that, during this kind of glow discharge, anomalous electric discharge (arcing) takes place for one cause or another. When arcing which is large in amount of current change (large in arc current) locally takes place between electrodes, there will be induced a problem of occurrence of splashes or particles, resulting in failure of good film forming. Therefore, in the above-mentioned bipolar pulsed power supply, there is provided a detection circuit which detects an output current from a bridge circuit. When the output current as detected by this detection circuit has exceeded a steady output current value, the switching element in operation is switched to thereby once cut off the output to the electrode in question. Once the overcurrent has calmed down and the output current value becomes near the steady output current value, the output to the electrode in question is resumed (see patent document 1). In other words, in this bipolar pulsed power supply, when the output current varies beyond a certain range, it is taken or recognized as a pre-stage phenomenon (micro-arc) of arcing. Then, by performing the processing of extinguishing the arcing, the generation of arcing that is large in the amount of current change can be suppressed.    Patent Document 1: Japanese patent No. 3,639,605 (see, e.g., claim 1, the description in paragraph No. 0016).